A group calling itself the Syrian Electronic Army is claiming that it successfully hacked the official Twitter account of the Associated Press and is responsible for a tweet that briefly wiped billions off the Dow Jones Industrial Average on Tuesday.

The tweet, issued from AP's main account, warned that there had been two explosions in the White House, one of which had injured Barack Obama. The Dow dropped over 140 points on the news, before rebounding minutes later after the administration denied the story.

"The president is fine," said White House spokesman Jay Carney at Tuesday afternoon's press briefing. "I was just with him."

AP has since confirmed that its account had been hacked. It has disabled its Twitter accounts for the time being and is warning people to disregard the earlier tweet and to be on their guard against further false messages.

The Syrian Electronic Army, a group of hackers who support the embattled president Assad in the long-running Syrian civil war, claimed responsibility for the attack. Over the last few days it has been targeting the Twitter accounts of Western media organizations and using them to spread misinformation and malware.

"AP Twitter feed was hacked today by the Syrian Electronic Army. SEA published a false news about an explosion in the whitehouse and Obama got injured. This small tweet created some chaos in the United States in addition to a decline in some U.S. stocks," the group said on their website.

This isn't the first time the stock market has got its panties in a bunch over misinformation released online. In 2008, Apple lost over 5 per cent of its value following a false report that Steve Jobs had suffered a heart attack.

But the speed of Tuesday's drop has caused some to point the finger at the shadowy world of high-frequency traders (HFT), who now account for over 60 per cent of US stock market buy and sell orders. HFT systems will place millions of orders at a time to gain pennies from arbitrage on stock prices, and this type of trading is particularly vulnerable to spoofing.

"High-frequency traders cancel their orders on even one little tweet. They provide so much liquidity and don't have obligations like market makers did in the past. We need other participants to make sure this kind of volatility doesn't happen and we don't [have them] anymore," Dennis Dick, proprietary trader at Bright Trading LLC, told Reuters. ®